This book discusses many advances in optical physic, and is aimed at advanced undergraduates taking courses in atomic physics, or graduate students in the fields of lasers, astrophysics, and physical chemistry. The book is intended mainly for experimentalists, and the interaction of electromagnetic radiation with free atoms is introduced using classical or semi-classical calculations wherever possible. Topics discussed include the spontaneous emission of radiation, stimulated transitions and the properties of gas and turnable dye lasers, and the physics and applications of resonance fluorescence, optical double resonance, optical pumping, and atomic beam magnetic resonance experiments.